Steam turbine

ABSTRACT

The invention relates to a steam turbine (10), in particular for using the waste heat of an internal combustion engine (2), comprising at least one rotor (26) and at least one stator (20), said stator (20) comprising at least two nozzles (22) which are arranged in parallel in relation to each other. The nozzles (22) are designed for different load points of the rotor (26) and can be switched on and off independently from each other.

BACKGROUND OF THE INVENTION

The invention relates to a steam turbine, in particular for using thewaste heat of an internal combustion engine.

A steam turbine is known from the German patent application DE 42 14 775A1, which can be operated at different load conditions. Said steamturbine is characterized by a plurality of nozzle groups of the samedesign in the stator. In order to control the steam turbine at differentload demands, the steam inflow to each nozzle group is adjusted with acontrol valve. In the case of a low load demand, only one nozzle or onenozzle group is activated. When the power requirements increase, steamis applied to one nozzle group after the other. The control of the steamsupply takes place thereby by means of the control slots of a rotaryslide valve. It is also common to employ automatic regulators.

SUMMARY OF THE INVENTION

The steam turbine according to the invention has the advantage that aparticularly large power spectrum can be covered by the steam turbinethrough the use of nozzles, which are designed for different load pointsand can be switched on and off independently from each other.

The different designs of the nozzles can be simply and advantageouslypredefined by the geometry thereof, the area ratio between the narrowestnozzle cross section and the outlet cross section, the amount ofunblocked flow cross section and/or the angle of inclination of thenozzle with respect to the rotor.

The requirement for a large power spectrum occurs especially in steamturbines which are employed for using the waste heat of an internalcombustion engine that is operated in a motor vehicle. It is thusparticularly advantageous for the different operating points of theinternal combustion engine to correspond to the different load points ofthe rotor. The boundary conditions (steam quantity, temperature,pressure) vary at the inlet into the stator as a function of therespective operating point of the internal combustion engine. An optimalutilization of the energy provided by the internal combustion engine canbe achieved by switching differently designed nozzles on and off becausesaid nozzles are adapted to the respective boundary conditions.

A particular advantage results if a nozzle for a high load point of therotor and another nozzle for a low load point of the rotor areintegrated into the stator. A particularly broad power spectrum can becovered with only a few nozzles by means of this measure. This resultsby virtue of the fact that only the nozzle having the design for the lowload points can be switched on for low load points of the internalcombustion engine while the other nozzle is switched off. In contrastthereto, only the nozzle having the design for high load points can beswitched on for high load points of the internal combustion engine whilethe other nozzle is switched off. Further load points of the internalcombustion engine can be covered by a combination of both nozzles. As aresult of the small number of nozzles, costs can be saved in theconstruction of the steam turbine and a broad power spectrum of theinternal combustion engine can be covered at the same time.

Laval nozzles are expediently employed for the acceleration of the steamin the stator. By the use of said Laval nozzles, the steam can therebybe accelerated from ultrasonic velocity to supersonic velocity. Onaccount of the high velocities, a particularly high power output of thesteam turbine can be achieved.

The use of partially impinged turbines is advantageous because thediameter of the rotor can be increased by means of the partialimpingement, and design sizes of turbines which are small and difficultto implement can thereby be avoided.

A further advantage results if the nozzles of the steam turbine areswitched on and off via switching equipment consisting of control valvesor aperture plates. Such switching equipment makes a plurality ofpossible nozzle combinations available.

Switching equipment, which is controlled via a pressure differencepresent at the stator, is particularly advantageous because theswitching of the nozzles on and off can be optimally adapted to theprevailing boundary conditions. It is useful for the switching equipmentto be actuated via a servomotor, in particular a multiphase motor, asthis allows for a simple and cost effective implementation option.

A nozzle can be advantageously employed as a nozzle bypass, which guidesthe steam without acceleration onto the rotor in order to allow steam toslowly flow through the rotor during warm-up or in order not to generateany power during deceleration of the internal combustion engine. Abypass implemented in this form is much more cost effective than abypass which leads the steam past the steam turbine. By allowing steamto slowly flow through the turbine during warm-up, damage to the rotorsdue to retrograde condensation, which is caused by steam having a lowerquality, is furthermore prevented. In addition, problems due to freezingon the rotors resulting from the warm steam prior to startup of thesteam turbine can be eliminated.

It is thereby particularly advantageous if the nozzle, which serves asthe nozzle bypass, changes the direction of the steam jet in such amanner that a resulting torque is not produced at the rotor. In sodoing, a power output of the steam turbine during deceleration isprevented.

In steam turbines, which have a plurality of stages consisting ofstators and rotors disposed one behind the other, it is advantageous ifthe nozzles of the downstream stages consisting of stator and rotor aredisposed in such a manner that said nozzles correspond in the disposaland design thereof with the nozzles of the first stage consisting ofstator and rotor. By means of this disposal, additional switchingequipment in the downstream stages can be avoided and costs aretherefore saved.

The employment of a steam turbine having the previously mentionedfeatures is particularly advantageous if said turbine is disposed in acircuit comprising a feed pump, heat exchanger and condenser and theheat exchanger serves the purpose of using the waste heat of an internalcombustion engine and produces the steam which is supplied to thenozzles of the stator. This is the case because a particularly broadpower spectrum results from this disposal.

BRIEF DESCRIPTION OF THE DRAWINGS

Exemplary embodiments of the invention are depicted in the drawings andexplained in detail in the description below. In the drawings:

FIG. 1 shows a steam turbine in a schematic depiction according to afirst exemplary embodiment.

FIG. 2 shows a Laval nozzle in perspective depiction.

FIG. 3 shows a steam turbine in schematic depiction according to asecond exemplary embodiment and

FIG. 4 shows a steam turbine comprising a circuit in a schematicdepiction.

DETAILED DESCRIPTION

FIGS. 1 and 3 show a steam turbine 10 in a schematic depictioncomprising a rotor 26, a stator 20 and switching equipment 28. At leasttwo nozzles 22 are disposed in the stator 20, which convert thepotential energy of the steam into kinetic energy in said stator 20.

The nozzles 22 are disposed in parallel in relation to each another inthe stator 20; and therefore the steam enters in a plane which is thesame for all nozzles 22 and is perpendicular to the main flow directionand leaves said nozzles 22 in another plane which is perpendicular tothe main flow direction. The nozzles 22 are circularly disposed in thestator 20 This can relate to a fully impinged steam turbine 10, in whichsaid nozzles are disposed around the entire stator 20 or to a partiallyimpinged steam turbine 10, in which said nozzles 22 occupy only parts ora sector of the circle of the said stator 20.

The nozzles 22 are designed for different load points of the rotor 26,wherein at least one of the nozzles 22 is designed for a high load pointof the rotor 26 and at least one of the nozzles 22 is designed for a lowload point of said rotor 26.

The different design of the nozzles 22 is primarily determined by thegeometry thereof, the amount of unblocked flow cross section, the arearatio between the narrowest nozzle cross section and the outlet crosssection and/or the angle of inclination of the nozzle 22 with respect tothe rotor 26. The design of the individual nozzles 22 is determined onthe basis of the operating conditions encountered, such as mass flow,temperature and pressure conditions. Said operating conditions fluctuateparticularly sharply in a steam turbine which is used for the recoveryof waste heat of an internal combustion engine.

The nozzles 22 are preferably Laval nozzles 24, as they are depicted inFIG. 2, and guide the steam in an accelerated manner onto the rotor 26of the steam turbine 10. The Laval nozzles 24 are configured asrectangular channels having a convergent and divergent cross-sectionalprofile. Due to their special design, Laval nozzles 24 are capable ofaccelerating gas flows from subsonic to supersonic velocities.

Provision can be made for further nozzles 22 for other load points ofthe rotor 26 or for a plurality of nozzles 22 for the same load point ofthe rotor 26. The nozzles 22 can be disposed in nozzle groups orindividually in the stator 20.

Switching equipment 28 is disposed upstream of the stator 20, saidswitching equipment switching the nozzles 22 in said stator 20independently from each other. By means of the switching equipment 28,each nozzle 22 can be opened alone while the other nozzles 22 areclosed, or a plurality of nozzles 22 can be opened simultaneously. Ifthe nozzles 22 are disposed in nozzle groups, entire nozzle groups canalso be opened or closed via the switching equipment 28.

The switching equipment 28 can consist of control valves or of anaperture plate and can be disposed in front of or behind the stator 20.The switching equipment 28 can be controlled via a pressure differenceprevailing at the stator 28. As a function of the prevailing pressuredifference, one or a plurality of nozzles 22 adapted to this boundarycondition are activated while other nozzles 22 are closed. The switchingequipment 28 can be actuated via a servomotor, in particular amultiphase motor.

If an aperture plate is provided, the actuation of the switchingequipment 28 can then actively take place by means of a servomotor orpassively by using the prevailing pressure difference.

A further exemplary embodiment is depicted in FIG. 3, in which a furthernozzle is provided, which serves as a nozzle bypass 32, beside thenozzles 22 which serve to accelerate the steam onto the rotor 26. Saidnozzle bypass 32 is not embodied as a Laval nozzle 24 because the nozzlebypass 32 is to guide the steam without acceleration onto the rotor 26.Said nozzle bypass 32 has a large flow cross section in comparison toother nozzles 22; and therefore the pressure in the high pressure partupstream of the steam turbine 10 reduces very quickly and the steamachieves only very low flow velocities when entering the rotor 26. Dueto the low flow velocities, no significant power output is achieved inthe rotor 26.

The power output of the rotor 26 can be still further reduced if thenozzle bypass 32 changes the direction of the steam jet escaping fromthe nozzle bypass 32 in such a manner that no resulting torque isproduced. This can be brought about by said steam jet flowing againstthe rotor 26 in the axial direction or in the reverse direction ofrotation.

The steam turbine 10 can also be embodied as a multistage steam turbine10, in which a plurality of stages consisting of stators 20 and rotors26 is disposed one behind the other.

In each of the turbine stages, the nozzles 22 of the rotor 20 can beswitched on and off via switching equipment 28 and corresponding to thetwo exemplary embodiments pursuant to FIG. 1 and FIG. 3.

Alternatively switching equipment 28 for controlling the nozzles 22 canbe situated only in the first stage of the steam turbine 10, whichconsists of stator 20 and rotor 26 and is situated directly behind thesteam source. The nozzles 22 of the downstream stages consisting ofstator 20 and rotor 26 can be arranged in such a manner that saidnozzles correspond from the positioning thereof to the nozzles 22 of thefirst stage. In so doing, the steam jet of the nozzle 22, which isreleased in the first stage, should only enter into the correspondingnozzle 22 of the second stage. The corresponding nozzles 22 are designedsuch that they achieve an optimal degree of efficiency at the prevailingboundary conditions.

The steam turbine 10 is particularly suited for the recovery of wasteheat in applications in motor vehicles. The steam turbine 10 of theinvention is however also suited for other applications.

FIG. 4 shows a steam turbine 10 according to one of the precedingexemplary embodiments in a circuit 4 for the recovery of waste heat ofan internal combustion engine 2. A heat exchanger 8, a condenser 12, afeed pump 6 and the steam turbine 10 are disposed in the circuit 4containing a circulating working medium.

The internal combustion engine 2 burns fuel in order to producemechanical energy. The exhaust gases ensuing from this process aredischarged via an exhaust gas system, in which an exhaust gas catalystcan be disposed. A duct section of the exhaust gas system is led througha heat exchanger 8. Heat energy from the exhaust gases or the exhaustgas recirculation is given off to the working medium in the heatexchanger 8 so that said working medium can be evaporated andsuperheated in said heat exchanger 8.

The heat exchanger 8 of the circuit 4 is connected via a line to thesteam turbine 10. The evaporated working medium flows via the line tosaid steam turbine 10 and drives the same. Said steam turbine 10 has anoutput shaft 11, via which said steam turbine 10 is connected to a load.In this way, mechanical energy can, for example, be transferred to adrive train or used to drive an electrical generator, a pump orsomething similar. After flowing through said steam turbine 10, theworking medium is led via a line to a condenser 12. The working mediumwhich was expanded via said steam turbine 10 is cooled in the condenser12 and condenses. Said condenser 12 can be connected to a coolingcircuit. The working medium liquefied in said condenser 12 istransported via a line from a feed pump 6 into the line to the heatexchanger 8.

A flow direction of the working medium through the circuit 4 is providedby the feed pump 6. Heat energy, which can be released in the form ofmechanical energy to the shaft 11, can therefore be continuouslyextracted via the heat exchanger 2 from the exhaust gases and theconstituent parts of the exhaust gas recirculation of the internalcombustion engine 2.

Water or another liquid, which corresponds to the thermodynamicrequirements, can be used as the working medium. The working mediumexperiences thermodynamic changes in state when flowing through thecircuit 4. In the liquid phase, said working medium is brought by thefeed pump 6 to the pressure level required for evaporation. The heatenergy of the exhaust gas is subsequently given off to said workingmedium via the heat exchanger 8. In so doing, said working medium isisobarically evaporated and subsequently superheated. The steam is thenadiabatically expanded in the steam turbine 10. In so doing, mechanicalenergy is obtained and transferred to the shaft 11. Said working mediumis then cooled in the condenser 12, liquefied and supplied again to thefeed pump 6.

As a function of the operating point of the internal combustion engine2, a variable amount of waste heat is provided to the heat exchanger 8.The heat exchanger 8 produces the steam, which is available to the steamturbine 10. The steam turbine 10 has to work as a function of theoperating point of the internal combustion engine 2 with other boundaryconditions (amount of steam, temperature, pressure) and adaptaccordingly to the load points thereof. This takes place by switchingthe nozzles 22 in the stator 20 of the steam turbine 10 on and off,which nozzles correspond to the different load points of the internalcombustion engine 2.

1. A steam turbine (10), comprising at least one rotor (26) and at leastone stator (20), said stator (20) comprising at least two nozzles (22)which are arranged in parallel in relation to each other, characterizedin that the nozzles (22) are designed for different load points of therotor (26) and can be switched on and off independently from each other.2. The steam turbine (10) according to claim 1, wherein the steamturbine uses the waste heat of an internal combustion engine, andcharacterized in that the different load points of the rotor (26)correspond to different operating points of the internal combustionengine (2).
 3. The steam turbine (10) according to claim 1,characterized in that the different design of the nozzles (22) isdefined by at least one of a geometry thereof, an amount of unblockedflow cross section and an angle of inclination of the nozzle (22) withrespect to the rotor (26).
 4. The steam turbine (10) according to claim1, characterized in that one of the nozzles (22) is designed for a lowload point of the rotor (26) and another of the nozzles (22) is designedfor a high load point of the rotor (26).
 5. The steam turbine (10)according to claim 1, characterized in that at least one of the nozzles(22) is a Laval nozzle (24).
 6. The steam turbine (10) according toclaim 1, characterized in that the rotor (26) is partially impinged withsteam.
 7. The steam turbine (10) according to claim 1, characterized inthat the nozzles (22) are switched on and off via switching equipment(28) consisting of control valves (30) or aperture plates.
 8. The steamturbine (10) according to claim 7, characterized in that the switchingequipment (28) is controlled via a pressure difference prevailing at thestator (20).
 9. The steam turbine (10) according to claim 1,characterized in that one of the nozzles (22) serves as a nozzle bypass(32), which guides the steam without acceleration onto the rotor (26).10. The steam turbine (10) according to claim 9, characterized in thatthe nozzle (22) which serves as the nozzle bypass (32) changes a steamjet in such a manner that no resulting torque is produced.
 11. The steamturbine (10) according to claim 1, characterized in that a plurality ofstages consisting of stators (20) and rotors (26) is disposed one behindthe other.
 12. The steam turbine (10) according to claim 10,characterized in that the nozzles (22) of the downstream stagesconsisting of stator (20) and rotor (26) are disposed in such a mannerthat said nozzles correspond in a configuration thereof to the nozzles(22) of a first stage consisting of stator (20) and rotor (26).
 13. Thesteam turbine (10) according to claim 1 wherein the steam turbine usesthe waste heat of an internal combustion engine, and comprising acircuit (4), characterized in that a feed pump (6), a heat exchanger (8)and a condenser (12) are disposed in the circuit (4) and in that theheat exchanger (8) serves in using the waste heat of an internalcombustion engine (2) and produces the steam which is supplied to thenozzles (22) of the stator (20).
 14. The steam turbine (10) according toclaim 1, characterized in that the different design of the nozzles (22)is defined by the geometry thereof.
 15. The steam turbine (10) accordingto claim 1, characterized in that the different design of the nozzles(22) is defined by an amount of unblocked flow cross section.
 16. Thesteam turbine (10) according to claim 1, characterized in that thedifferent design of the nozzles (22) is defined by an angle ofinclination of the nozzle (22) with respect to the rotor (26).